In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures which are slightly lower than temperatures normally injurious to healthy cells. These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill it. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, kidney, lung, brain, and liver.
Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical, which may be inserted into a patient for the treatment of tumors by heating the tissue for a period of time sufficient to cause cell death and necrosis in the tissue region of interest. Such microwave probes may be advanced into the patient, e.g., laparoscopically or percutaneously, and into or adjacent to the tumor to be treated. The probe is sometimes surrounded by a dielectric sleeve.
However, in transmitting the microwave energy into the tissue, the outer surface of the microwave antennas typically may heat up and unnecessarily necrose healthy tissue immediately adjacent the antenna outer surface. To prevent the charring of adjacent tissue, several different cooling methodologies are conventionally employed. For instance, some microwave antennas utilize balloons which are inflatable around selective portions of the antenna to cool the surrounding tissue. Thus, the complications associated with tissue damaged by the application of microwave radiation to the region is minimized. Typically, the cooling system and the tissue are maintained in contact to ensure adequate cooling of the tissue.
Other devices attempt to limit the heating of tissue adjacent the antenna by selectively blocking the propagation of the microwave field generated by the antenna. These cooling systems also protect surrounding healthy tissues by selectively absorbing microwave radiation and minimize thermal damage to the tissue by absorbing heat energy.
However, in order for microwave ablation to become a truly effective tool for the laparoscopic and/or percutaneous treatment of tumors, an effective microwave antenna should be implemented to efficiently transfer energy to the targeted tissue region while minimizing unnecessary tissue damage adjacent to the antenna outer surface. Moreover, the cooling aspects along the antenna should be controllable to allow for different regions of cooling as well as to allow for the coagulation of adjacent tissue along selected regions of the antenna, if desired.